1. Field of the Invention
The present invention relates to a projector which separates a luminous flux from a light source into a plurality of partial luminous fluxes and modulates the plurality of partial luminous fluxes according to image information by means of an electro-optic device.
2. Description of Related Art
As a projector capable of projecting and displaying a color image, in addition to a projector of a three-plate type provided with an electro-optic device for each of three color lights, a projector of a single-plate type forming a color image by means of a single electro-optic device has been put to practical use.
A projector of a single-plate type has an advantage of making it possible to easily make a projector apparatus smaller in size and lower in cost.
There are various forms of single-plate type projectors, and among them a single-plate type projector which irradiates a single liquid crystal display device (electro-optic device) provided with a microlens array with color lights obtained by color separation by means of three dichroic mirrors (a color separation optical element) arranged at specific positions like a color liquid crystal display device disclosed in Japanese Patent Laid-Open Publication No. Hei 4-60,538 is well known (hereinafter an electro-optic device of such a composition is called an electro-optic device of a spatial color separation type). A projector of such a form attracts public attention in that it has a high efficiency of light utilization and can easily provide a bright projected image in spite of its single-plate type.
Further, a single-plate type projector as described above is contrived so as to arrange various optical elements such as a luminous flux separation optical element, a polarization transforming element, a color separation optical element and the like in an optical path from a light source to an electro-optic devise, utilize light of the light source without waste, and thereby form a projected image being not irregular in brightness and color.
A luminous flux separation optical element is an optical element which separates a luminous flux from a light source into a plurality of partial luminous fluxes, forms a plurality of light source images in a virtual plane nearly perpendicular to a virtual optical axis of illumination passing nearly the center of the said luminous flux separation optical element, superposes luminous fluxes from the plurality of light source images on an electro-optic device by considering them as pseudo-light sources, and thereby obtains illuminating luminous fluxes being uniform in distribution of intensity. Concretely, as a luminous flux separation optical element, a bar-type optical conductor which reflects a luminous flux inputted from the entrance end by plural pairs of reflecting faces, separates the luminous flux into a plurality of partial luminous fluxes according to different positions of reflection and outputs them from the exit end, a lens array having a plurality of lenses arranged in a plane opposite to the pixel area of an electro-optic device, or the like is adopted.
A polarization transforming element is an optical element which separates an incident luminous flux being random in direction of polarization direction into two polarized luminous fluxes, rotates the polarization direction at least one of the two polarized luminous fluxes, and thereby outputs luminous fluxes being uniform in direction of polarization. Concretely, a polarization transforming element comprises a polarization separating film which transmits one of two polarized luminous fluxes being different in direction of polarization from each other and reflects the other, a reflecting film which reflects the other polarized luminous flux separated, and a retardation plate which turns either of the two polarized luminous fluxes in direction of polarization.
A color separation optical element is an optical element which separates an incident luminous flux into a plurality of color lights such as R, G, B and the like for example, in which three dichroic mirrors to respectively reflect red, green and blue lights are arranged at different angles from one another with respect to the direction of incidence of a luminous flux and the respective color lights separated by the three dichroic mirrors are outputted at different angles from one another.
An electro-optic device of a spatial color separation type modulates each of luminous fluxes separated by said color separation optical element according to its image information for each color light and forms a color image. In the electro-optic device, three rectangular sub-pixels respectively corresponding to R, G and B lights are arranged side by side, and one microlens is formed for these three sub-pixels. The respective color lights incident upon the microlens at different angles are condensed by the microlens, enter their corresponding sub-pixels and are modulated for their respective colors and then outputted through a projection lens to form a color image projected.
Thus, a pixel area obtained by combining R, G and B sub-pixels in an electro-optic device is formed into a nearly square shape, and a sub-pixel to be modulated for each color light is formed by dividing said nearly square-shaped pixel area along the direction of incidence of each color light. In other words, a sub-pixel is formed into the shape of a rectangle having its short sides in the direction of color separation performed by the color separation optical system.
However, since a sub-pixel for each color light is formed into the shape of a rectangle in a single-plate type projector of such a structure, when a inclined light in the short-side direction of the rectangle is entered, a different color light is mixed into an adjacent sub-pixel and the color light leaks to a sub-pixel for another color light to generate a color mixture, and as a result, an image projected on a screen is degraded in contrast and color reproducibility. In a single-plate type projector, therefore, it is important how the angular distribution of lights incident on an electro-optic device in the short-side direction. is controlled.
An object of the present invention is to provide a single-plate type projector using an electro-optic device of a spatial color separation type, said projector preventing a color mixture and being high in contrast and color reproducibility.
(1) A projector according to the present invention is a projector comprising;
a luminous flux separation optical element that separates a luminous flux from a light source into a plurality of partial luminous fluxes,
a polarization transforming element that separates each of said plurality of partial luminous fluxes into two polarized luminous fluxes and then converts the two luminous fluxes into a single polarized luminous fluxes being uniform in direction of polarization,
an electro-optic device that modulates an illuminating luminous flux outputted from said polarization transforming element, said electro-optic device having a plurality of long and narrow pixels respectively corresponding to color lights and being arranged adjacently to one another, and
a projection lens that projects a luminous flux modulated by said electro-optic device, and
a direction of polarization separation of said plurality of partial luminous fluxes performed by said polarization transforming element coincides nearly with the long-side direction of said pixel.
In case of disposing a polarization transforming element between a light source and an electro-optic device for the purpose of improving the efficiency of utilizing light, an angular distribution of light is spread in direction of polarization separation due to separation of polarization by the polarization transforming element. In the present invention, however, since the direction of polarization separation by the polarization transforming element corresponds to the long-side direction of a pixel in an electro-optic device, an angular distribution of illuminating fluxes is spread in the long-side direction of a pixel but is little spread in the short-side direction of the pixel. Therefore, it is possible to reduce a color mixture (leak of light) caused by a different color light to enter an adjacent pixel and attain a projected image being high in contrast and excellent in color reproducibility.
(2) As for an electro-optic device, it is preferable that the present invention is applied to an electro-optic device of a transmission type which modulates an incident luminous flux with said pixels and outputs the luminous flux at the opposite side to the entrance side.
It is a matter of course that the present invention can be also applied to an electro-optic device of a reflection type which modulates an incident luminous flux and then outputs the luminous flux at the entrance side. In such a case, however, since polarization selecting elements such as polarization beam splitters and the like are disposed between an electro-optic device and an illuminator and between an electro-optic device and a projection lens, it is necessary to optimize characteristics of the polarization transforming element and the luminous flux separation optical element in order to keep the characteristics of the polarization selecting element. On the other hand, since an electro-optic device of a transmission type does not need such a polarization selecting element, it has an advantage of easily forming a projector in no consideration of the characteristics of a polarization selecting element.
(3) A luminous separation optical element is preferably composed so as to form a plurality of light source images at intervals more narrow in the short-side direction of a pixel than the long-side direction.
By making more narrow the intervals between light source images in the short-side direction of a pixel, it is possible to surely reduce the expansion of an angular distribution of illuminating luminous fluxes in the short-side direction of a pixel. Accordingly, it is possible to reduce a color mixture caused by leak of light to an adjacent pixel and attain a projected image being very high in contrast and excellent in color reproducibility.
(3-1) As a luminous flux separation optical element, a rod can be adopted which reflects an incident luminous flux entered through the entrance end from a light source by plural pairs of reflecting faces, separates the luminous flux into a plurality of partial luminous fluxes, and outputs them from the exit end.
In this case, as such a rod it is possible to adopt a solid rod made of a material having an optical conductivity or a hollow rod made by forming light reflecting faces on the inner faces of a tube. Since a solid rod has a total reflection faces with no optical loss, it has an advantage of improving the efficiency of light utilization. Since a hollow rod makes an incident luminous flux entered from the entrance end reach the exit end through the air layer inside the rod, it has an advantage that a uniform illuminating luminous flux can be attained even by making comparatively short the distance between the entrance end and the exit end and further it is easier to manufacture than the solid rod.
In case of using a solid rod or a hollow rod, it is enough that at least two pairs of reflection faces being opposite to each other in the long-side direction and the short-side direction of a pixel, and the section of the rod may be in the shape of such a polygon having more sides than a tetragon as an octagon, a dodecagon and the like.
However, taking account of the efficiency of optical transmission from a light source to a luminous flux separation optical element, since the section of a luminous flux incident on the luminous flux separation optical element from the light source is nearly circular in shape, it is preferable that the shape of the entrance end of the rod is a square, and taking account of the efficiency of illumination to an electro-optic device, it is preferable that the shape of the exit end of the rod is nearly similar to the shape of a display area of the electro-optic device.
In case of adopting a rod as described above as a luminous flux separation optical element, a plurality of light source images can be formed at more narrow intervals in the short-side direction than the long-side direction of a pixel by inclining a pair of reflecting faces opposite to each other in the short-side direction of a pixel so as to be made gradually wider from the entrance end toward the exit end. Accordingly, it is possible to reduce a color mixture caused by leak of light to an adjacent pixel and attain a projected image being very high in contrast and excellent in color reproducibility.
And further, the interval between a pair of reflection faces of a rod being opposite to each other in the long-side direction of a pixel may be made gradually more narrow from the entrance end toward the exit end of the rod.
In this case, since the intervals between light source images in the long-side direction of pixels can be made wider, the interval between the polarization separation film of a polarization transforming element and the reflection face can be set as sufficiently taking account of the size of a light source image. Therefore, it is possible to improve the efficiency of polarization transformation in a polarization transforming element and, as a result, improve the efficiency of light utilization in a projector.
(3-2) As a luminous flux separation element, a lens array formed by arranging a plurality of lenses in the long-side direction and the short-side direction of a pixel in an electro-optic device can be adopted.
In this case, it is preferable that the light condensing characteristics of the plurality of lenses are set so as to form a plurality of light source images at more narrow intervals in the short-side direction of a pixel than the long-side direction. The extent of an angular distribution of illuminating luminous fluxes in the short-side direction of a pixel can he surely reduced by setting the light condensing characteristic of each lens in such a way. Accordingly, it is possible to reduce a color mixture caused by leak of light to an adjacent pixel and attain a projected image being very high in contrast and excellent in color reproducibility.
Hereupon, as a lens forming a lens array, a hologram lens or diffraction lens for condensing light by means of a holography or diffraction effect can be adopted in addition to a general lens whose surface is formed into the shape of a curve.
In case of adopting a lens array as a luminous flux separation optical element, it is preferable that a plurality of lenses each are similar in shape to a display area of an electro-optic device. An image formed on a lens of a lens array is superposed on a display area being a single area to be illuminated in the electro-optic device. Accordingly, since a luminous flux outputted from the lens can be introduced into the display area with no waste by making the shape of a lens nearly similar to the shape of a display area of the electro-optic device, the efficiency of illumination can be improved.
And it is preferable that some or all of a plurality of lenses forming a lens array are eccentric lenses. Namely, since a light source image can be formed at a position other than the physical center of each lens by using eccentric lenses as some or all of lenses, it is possible to freely control the intervals between a plurality of light source images formed in a virtual plane.
(4) In case of using a lens array as a luminous flux separation optical element, it is preferable to dispose a reducing optical system in an optical path between a light source and a polarization transforming element. And by reducing the total sectional dimensions of an illuminating luminous flux in the short-side direction of a pixel, it is possible to further reduce the extent of an angular distribution of the illuminating luminous flux in the short-side direction of a pixel.
Accordingly, it is possible to reduce a color mixture caused by leak of light to an adjacent pixel and attain a projected image being very high in contrast and excellent in color reproducibility. And since the total diameter of a luminous flux to illuminate an area to be illuminated can be made smaller, it is possible to use a projection lens being small in aperture and inexpensive in cost as a projection lens disposed at the exit face side of an electro-optic device and make a projector low in cost.
And in this case, not only the sectional dimensions in the short-side direction of a pixel but also the sectional dimensions in the long-side direction of a pixel may be reduced. In such a case, a color mixture caused by leak of light to an adjacent pixel can be furthermore reduced.
Such a reducing optical system can be composed of at least one convex lens disposed at one of the entrance side and the exit side of a lens array and at least one concave lens disposed at the entrance side of a polarization transforming element. And in case of making small the sectional dimension of an illuminating luminous flux only in the short-side direction of a pixel, cylindrical lenses can be used as a concave lens and a convex lens. The convex lens and concave lens each can be composed of a single lens, but considering reduction of their optical aberrations, it is preferable that each of them is a combination lens obtained by combining a plurality of lenses.
(5) In a projector as described above, a reducing optical system for reducing the total sectional dimensions of an illuminating luminous flux in the short-side direction of a pixel can be used between a polarization transforming element and an electro-optic device.
Such a reducing optical system can be composed of a single concave lens, but taking account of reduction of its optical aberrations, it is preferable that the concave lens is composed of a combination lens obtained by combining a plurality of lenses. And in case of making small the sectional dimension of an illuminating luminous flux only in the short-side direction of a pixel, cylindrical lenses can be used as a convex lens and a concave lens. The same effect as the case (4) described above can be obtained also by using such a reducing optical system.
And in this case also, the sectional dimensions may be reduced not only in the short-side direction of a pixel but also in the long-side direction of a pixel. In such a case, a general curved lens being axially symmetric can be used as each of the concave and convex lenses.
(6) As a polarization transforming element, it is preferable to adopt a polarization transforming element which comprises a polarization separating film that transmits one of the two polarized luminous fluxes and reflecting the others, a reflecting film that reflects the other kind of polarized luminous fluxes, and a retardation plate (xc2xd-retardation plate or the like) that makes the two polarized luminous fluxes uniform in direction of polarization.
In a composition having such a polarization transforming element, in case that a first imaging optical system arranging the entrance end of a luminous flux separation optical element and a polarization transforming element in a conjugate relation to each other, and a second imaging optical system arranging the exit end of the luminous flux separation optical element and an electro-optic device in a conjugate relation to each other are formed, it is preferable that the conjugate ratio of the second imaging optical system is not less than 4.
The angular distribution of secondary light source images on the exit end of a luminous flux separation optical element is determined by the shape of a side face of the luminous flux separation optical element, for example, the shape of a tapered side face in case that the luminous flux separation optical element has a pair of tapered sides opposite to each other being made wider toward the light source, the F-number of the light source, the angular distribution specific to the light source and the like. And generally, the greater the conjugate ratio is, the more surely the parallelism of lights to be imaged on the electro-optic device can be obtained. The parallelism of the lights varies depending on the sub-pixel pitch of each color light on the electro-optic device, and it is preferable that the conjugate ratio for pixels having a fine pitch of about 10 xcexcm is not less than 4, and a conjugate ratio of not less than 4 makes it possible to secure the parallelism among the respective color lights, prevent a color light from leaking to an adjacent pixel of another color light and thereby more surely prevent occurrence of mixture of colors in a projected image.
In case that such a second imaging optical system comprises a superposing lens to be disposed at the hind stage of a polarization transforming element and a parallelizing lens to be disposed at the fore stage of an electro-optic device, it is preferable that the color separation optical system is disposed between the superposing lens and the parallelizing lens.
By setting the conjugate ratio of the second imaging optical system as not less than 4, the parallelism among the respective color lights incident on the electro-optic device can be secured, and a certain degree of distance is formed between the superposing lens and the parallelizing lens. Accordingly, by disposing a color separation optical system provided with a plurality of mirrors at such a position and bending a luminous flux, it is possible to secure a necessary conjugate ratio even in a small space and make a projector smaller in size by disposing a color separation optical element without influencing another optical system.
(7) A projector according to the present invention may be a single-plate type projector comprising;
a light source,
a color separation optical system that separates a luminous flux outputted from said light source into a plurality of color lights, said color separation optical system comprises a plurality of mirrors;
an electro-optic device that modulates respectively the color lights according to their image information to form an optical image, and
a polarization transforming optical system provided at the fore stage of said color separation optical system, said polarization transforming optical system comprises a polarization separating film that transmits one of two polarized luminous fluxes and reflects the other, a reflecting film that reflects a polarized luminous flux reflected by said polarization separating film nearly in the same direction as said a single polarized luminous fluxes, and a retardation plate that makes said two polarized luminous fluxes uniform in direction of polarization, the direction in which said other polarized luminous flux is reflected by said polarization separating film is nearly perpendicular to the plane determined by the central axis of a luminous flux incident on said mirror and the central axis of the luminous flux reflected by said mirror.
According to the present invention as described above, since the direction in which the other luminous flux is reflected by a polarization separating film is nearly perpendicular to the plane determined by the central axis of a luminous flux incident on a mirror and the central axis of the luminous flux reflected by the mirror, a luminous flux outputted through the polarization transforming optical system diverges in the directions perpendicular to the direction of color separation of a plurality of color lights. Since the output luminous flux spreads in the long-side direction of a rectangle-shaped sub-pixel of each color light in an electro-optic device, it is possible to reduce leak of light to an adjacent sub-pixel of another color light and thereby prevent mixture of colors from occurring in a projected image.
In the present invention, a luminous flux separation optical element comprising a pole-shaped optical conductor for separating a luminous flux from a light source into a plurality of partial luminous fluxes may be disposed at the fore stage of said polarization transforming optical system.
Said optical conductor is preferably provided with tapered side faces whose dimensions in the direction perpendicular to the plane determined by the central axis of a luminous flux incident on said mirror and the central axis of the luminous flux reflected by said mirror are made gradually wider from the exit end of said optical conductor toward the entrance end.
Each time a luminous flux which has entered an optical conductor from the entrance end of it repeats an internal reflection from such tapered side faces, the angles of incidence and reflection of the luminous flux at the tapered side faces become smaller. Accordingly, when tapered side faces in which the dimensions in the direction perpendicular to the plane determined by the central axes of incident and reflected luminous fluxes on and from a mirror forming a color separation optical system are made gradually wider from the exit end toward the entrance end are adopted, since the intervals between the tertiary light source images become larger, a luminous flux utilizable after polarization transformation is increased and therefore the efficiency of polarization transformation by a polarization transforming optical system is improved.
And it is preferable that a reflecting mirror that reflects and supplies an output luminous flux from said light source to the entrance end of said optical conductor is provided between said light source and said optical conductor. Here, it is preferable that the direction of incidence of a luminous flux incident on said reflecting mirror is made nearly parallel with the output direction of the luminous fluxes outputted from a plurality of mirrors forming a color separation optical system.
In case of supplying a luminous flux outputted from a light source to the entrance end of an optical conductor, the light of a lamp or the like is condensed on the entrance end of the optical conductor by means of a reflector, a lens and the like. Therefore, since said reflecting mirror can be made small by disposing a reflecting mirror midway in the course of condensation of an output luminous flux from a light source in such a manner, a projector can be made small in size. And since the optical path of an output luminous flux from a light source to a projection optical system can be made U-shaped by making the direction of incidence of a luminous flux incident on a reflecting mirror nearly parallel with the output direction of luminous fluxes from a plurality of mirrors forming a color separation optical system, a projector can be more advantageously made smaller in size.
And the other polarized luminous flux described above is preferably an s-polarized luminous flux to a polarization separating film, and this s-polarized luminous flux is preferably transformed into a p-polarized luminous flux by said retardation plate.
Since an s-polarized luminous flux is transformed into a p-polarized luminous flux by a polarization transforming optical system and thereby a luminous flux is incident on mirrors forming a color separation optical system disposed at the hind stage of the polarization transforming optical system as an s-polarized luminous flux, the efficiency of reflection of the mirrors is improved. It is possible to provide a projector having a high efficiency of utilization of light outputted from a light source system.
Further, it is conceivable that a polarization transforming optical system is provided with a plurality of polarization separating films arranged so that their reflecting faces are parallel to each other or arranged according to the state of divergence of an incident luminous flux.
In case of a polarization transforming optical system in which polarization separating films are arranged to be parallel to another, since its structure is simplified, it is possible to make it easy to manufacture such a polarization transforming optical system. And when the polarization separating films are arranged according to the state of divergence of an incident luminous flux, since a polarization separation and transformation can be efficiently performed according to a divergent luminous flux outputted from the exit end of an optical conductor, the polarization separation characteristic is improved.